1. Field of the Invention
The present invention relates to a rocker arm with a built-in hydraulic valve lifter for installation in the valve system of an internal combustion engine.
2. Description of the Prior Art
A well-known valve mechanism of an internal combustion engine is designed such that a rocker arm is pivotably connected to the rocker shaft and a cam engages one end of the rocker arm. The cam pivots the rocker arm so that the other end of the rocker arm operates the suction and exhaust valves.
In such a valve mechanism the rocker arm is provided with a built-in hydraulic valve lifter so that the gap created between the suction and exhaust valves and the rocker arm on account of the expansion/contraction of the suction and exhaust valves due to temperature fluctuations and the abrasive wear of the driving parts may be automatically absorbed, thereby maintaining a zero lash between the suction and exhaust valves and the rocker arm. The hydraulic valve lifter includes a lifter body with a slidable plunger inserted into a recess formed on the rocker arm. An oil chamber is defined between the recess and the plunger. An oil pressure chamber is defined between the plunger and the lifter body. A check valve is installed in a passage between the oil chamber and the oil pressure chamber to prevent a back flow of the oil from the oil pressure chamber into the oil chamber. An oil supply path for supplying the oil to the oil chamber runs through the rocker arm, and extends from the oil hole of the rocker shaft to the oil chamber of the hydraulic valve lifter.
In the conventional rocker arm with such a built-in hydraulic valve lifter, while the engine is not working and there is no supply of the oil from the oil pump, the suction path of the engine and the oil path of the rocker shaft are filled with air instead of oil. Therefore, when the engine is working and particularly when it starts, the air in the oil or the air filling the oil path flows with the oil into the oil chamber of the hydraulic valve lifter.
If the air in the oil chamber has no escape provided for it, then the air may go into the oil pressure chamber. If the air goes into the oil pressure chamber, the lifter body will have an erratic motion, resulting in a failure of the hydraulic valve lifter to perform its normal function.